The present invention relates to a method for separating flexible, flat objects, especially paper sheets, sheets of board, sheet metal panels, or the like, which objects are lifted upward from a stack and are thereby separated, and are then being transported away in a transport direction that runs horizontally or at least approximately horizontally.
It is known to lift flexible, flat objects, for example sheet metal panels, from a stack by means of a vacuum device applied over the entire area, and then to transport the objects horizontally in the transport direction, in order to feed them to further-processing. The number of objects lifted and transported per unit time may not be increased indefinitely, because at increasing speed, the risk that a number of objects will be lifted at the same time increases, when the following sheet metal panel adheres to the lifted object like a sheet metal panel, that is located at the top. In spite of remedial measures, for example lateral introduction of blown air in order to improve the process of separating the panels, multiple lifting cannot be avoided at very high speeds. In addition, in modern feeders which act on the leading edge, the lifting sucker has to be put down on the stack during the panel gap between two successive panels and has to attract the next panel by suction and lift it. In the process, at high speeds, the time available becomes too short to permit trouble-free and low-vibration transport.
An object of the invention is to provide a method for separating flexible, flat objects and which ensures free operation even with large numbers of objects per unit time.
According to the invention, for the purpose of lifting, an adhesive action is built up which progresses in the transport direction and attracts the object. Consequently, the flat object is not lifted over its entire surface area or its entire length but is lifted progressively, region by region, specifically in such a way that the adhesive action which effects the lifting progresses in the transport direction. The trailing edge of the flat object is lifted first. During further lifting, the regions of the object progressively forward of the trailing edge are lifted by the adhesive action that builds up progressively, until the leading edge is reached. During the lifting, the progressive adhesive action subjects the object to reversible, for example S-shaped, bending, so that as viewed in cross section, it is transferred into the lifted position in the form of a xe2x80x9cwavexe2x80x9d that runs from the trailing edge to the leading edge. Once the lifted position has been reached, the object is transported away in a transport direction that runs horizontally or approximately horizontally.
After one article has been transported away, the following article is lifted from the stack. However, lifting of the following article may also take place in a position while it is overlapping the previous article, that is, as soon as the previously lifted article has been transported away, even by a small amount, and even though there is still a partial overlap of the first article with the stack, the following article is lifted starting in the region of its trailing edge. Lifting therefore takes place in a region of each article, e.g. a panel, which has been exposed by the previously lifted panel being transported away. The progressive lifting of each following panel is coordinated with the transporting away of the previously lifted panel.
In a development of the invention, the adhesive action is provided as a vacuum action. Applied vacuum can lift flexible, flat objects made of any material. If the objects are ferromagnetic, it is also possible to achieve the adhesive action by a magnetic holding action. The disclosure herein essentially discusses vacuum action. However, this disclosure also applies to magnetic devices.
The invention further relates to an apparatus for separating flexible, flat objects, in particular paper sheets, sheets of board, sheet metal panels, or the like. The apparatus includes an adhesion device which lifts the objects upward from a stack, and a transport device that transports the lifted objects in a transport direction that runs horizontally or at least approximately horizontally. The adhesive action that attracts each object is built up progressively in the transport direction. Accordingly, first the trailing edge of the object is lifted from the stack by adhesive action in the region of the trailing edge of the object. Then the remaining regions of the object are lifted, progressively in the transport direction, on account of the adhesive action, of the adhesion device, which progresses in the transport direction.
In a preferred embodiment, the adhesion device has a plurality of suction elements, which are located beside one another in the transport direction and can be activated and deactivated one after another. Activation of a suction element lifts the associated region of the sheet metal, or the like, panel into the lifted position. If the suction action is powerful enough and/or the suction element is at a sufficiently short distance from the sheet metal panel, the lifting occurs via the suction action. Alternatively, however, a lifting device may lift the sheet metal panel to a higher level in the region of its trailing edge so that the suction elements can develop their action and hold the panel in this region. This lifting device may, for example, be a pneumatic device, that is a piston which has a suction device at its free end and is moved up and down pneumatically.
In a further embodiment, the adhesion device has at least one suction means, which extends in the transport direction and can be activated progressively, or deactivated in the opposite direction, by displacing a slider. The slider, for example, enables suction openings to be opened, or enables a suction chamber in the adhesion device to be enlarged or reduced in size. An essentially downwardly open suction chamber has a side wall that is formed by the slider. When the object is being lifted, the side wall is displaced in the transport direction, so that the suction chamber expands in the transport direction. The progressive attraction of the object by suction takes place on account of the concomitantly progressive expansion of the suction chamber.
In a further preferred embodiment, the adhesion device is displaced continuously or segment by segment in the transport direction and in the direction of the object for the purpose of lifting it. Consequently, the adhesion device is first lowered in the region of the trailing edge of the object, so that the adhesive action starts there, and the corresponding region of the article is lifted. The adjacent regions of the adhesion device are then displaced continuously or segment by segment in the direction of the object, so that these regions of the object are also gripped and lifted.
In particular, after lifting of one region of the object, the adhesion device moves away from the stack again in this region. Consequently, the corresponding region of the adhesion device returns to its initial position as soon as the article has been lifted in this region.
In another embodiment, the adhesion device has at least one suction means, which extends in the transport direction and has a suction chamber which can be divided by at least one dividing wall into part chambers. The dividing walls or regions thereof can be displaced in order to connect/isolate adjacent part chambers. Firstly, the suction chamber is subdivided into part chambers by the dividing walls. The part chambers that are assigned to the trailing edge of the sheet metal panel have vacuum applied to them. As a result, the flexible, flat object is lifted in this zone. The dividing walls are then progressively displaced, so that the part chambers communicate with one another, that is, the part chambers are connected together progressively as far as the leading edge of the sheet metal panel. They are gradually all supplied with vacuum. Because of this, they develop their adhesive action, so that the article is progressively and continuously lifted.
Moreover, it is advantageous if the adhesion device has a plurality of suction chambers/suction openings, which are located beside one another in the transport direction and which can be activated/deactivated one after another by a vacuum control device. The activation or deactivation can be carried out, for example, by a valve control system, which is located between a vacuum source and the suction chambers or suction openings.
It is advantageous for the adhesion device to have at least two suction belt sections, which are located adjacent to one another in the transport direction and which at the same time form the transport device. It is possible for the vacuum and drive of suction belt sections to be activated/deactivated one after another or simultaneously. By successively activating the vacuum, it is possible to develop the adhesive action and to lift the object progressively and then to transport the object away horizontally by means of the simultaneous activation of all the drives of the suction belt sections. Once the trailing edge of a sheet metal panel leaves a suction belt section, the section can be deactivated again. The deactivation takes place with regard to the drive, so that, to create an interleaved system of sheet metal panels, the following sheet metal panel can be lifted in the region of its trailing edge. The individual suction belt sections thus have lengths which are shorter than the longitudinal format (i.e., format as viewed in the transport direction) of the sheet metal panels.
It is advantageous if suction elements, which can preferably be activated/deactivated under control, are located between adjacent suction belt sections. It is also possible for these suction elements then to be used for the progressive lifting of the sheet metal panels.
According to a further embodiment, the adhesion device is a blown air device, which blows air essentially along the surface of the object to be lifted. Blowing air approximately parallel to the surface of the sheet metal panel produces a suction effect which lifts the sheet metal panel to a higher level. This action also takes place progressively, starting from the trailing edge and going as far as the leading edge.
In a preferred embodiment, the adhesion device is a vacuum device, having a blown air device such that the blown air at least partly cancels the vacuum action of the adhesion device. Therefore, if the vacuum device is supplied with blown air in a specific region, then the vacuum develops no effect there, and no lifting of a sheet metal panel occurs in this region. By controlling the blown air, i.e., it is possible to influence the intensity and/or the direction and/or the point of incidence of the blown air. The vacuum action, which is constant over the entire length of the sheet metal panel, is specifically influenced in such a way that it builds up progressively in the transport direction, so that the object is correspondingly progressively lifted.
Once the object has been lifted to a higher level over its entire length and area by the adhesion device, then it is transported away horizontally by means of a transport device, which preferably has controlled-drive and preferably controlled-vacuum suction belts.